1. Field of the Invention
The present invention relates to the field of power electronics. It relates in particular to a semiconductor component with turn-off facility comprising
(a) a semiconductor wafer containing a sequence of differently doped layers which are arranged between a cathode side and an anode side and form a gate-turn-off thyristor (GTO) by means of a gate;
(b) on the cathode side of the semiconductor wafer, a finely subdivided gate-cathode structure having a multiplicity of island-like cathode fingers which are surrounded by a gate region;
(c) a cathode metallization over the cathode fingers; PA1 (d) an anode metallization on the anode side of the semiconductor wafer; and
(e) an anode contact and a cathode contact which are pressed onto the anode metallization or, in a multiplicity of locally limited regions, onto the cathode metallization, respectively, for the purpose of making contact.
Such a semiconductor component is disclosed, for example, by the publication EP-A1 0, 254, 910.
2. Discussion of Background
In power electronics, semiconductor components which, unlike conventional thyristors, can be switched off directly via a gate, are acquiring increasing importance. Such GTO (gate turn-off) thyristors contain a multiplicity of small-area, parallel-connected individual thyristors, also called segments, on a large-area semiconductor wafer.
Each of these individual thyristors comprises, on the cathode side, a cathode finger which is surrounded by a continuous gate region and either itself projects out of the plane of the gate region, or is of planar construction and is provided with a cathode metallization which is elevated in certain regions. On the cathode side this therefore results in a stepped, finely subdivided structure, whereas the semiconductor wafer is not usually subdivided and is of planar construction on the anode side.
The fine, and consequently mechanically sensitive structures on the cathode side of a GTO result in problems when making contact or during installation of such components. These problems are attributable in particular to the different local pressure distribution on the anode side and cathode side of the pressed semiconductor wafer.
The publication mentioned in the preamble proposes, as a solution to these problems, a so-called "direct" pressure contact on which the semiconductor wafer with the GTO active section is provided with a metallization and is pressed with adequately high pressure in the installed state between large-area metal discs having low coefficients of thermal expansion (for example, Mo or W). In this case, the pressure reaches an order of magnitude of 10 MPa, based on the total component area.
Since, as already mentioned previously, a multiplicity of small-area segments is present on the cathode side of the GTO, but a continuous large area on the anode side, a typical ratio of anode area AA to cathode area AK of EQU AA/AK=2 . . . 10